1. Field of the Invention
The present invention relates to an optical disk player which uses light, such as a laser beam, to record and reproduce information on and from an optical disk.
2. Description of the Related Art
In an optical disk player which reproduces signals from a compact disk or a laser disk that has pits corresponding to recording signals recorded on its disk-shaped recording medium, a laser beam is focused on pits or non-pit portions and a change in the intensity of the reflected light therefrom is detected to reproduce the recorded signals. The optical detection system in this optical disk player has a limitation on the cutoff spatial frequency 2 NA/.lambda. (wherein NA represents the number of apertures of the objective lens; and .lambda. represents the wavelength of the laser beam). To improve the spatial resolution to thereby increase the surface density of the recording film, it is essential to increase the number of apertures of the objective lens and shorten the wavelength of the laser beam.
As an example of an optical disk player designed to improve the spatial resolution, there has been proposed an apparatus which employs apodization or super resolution (as disclosed in Japanese Patent Application No. 12625/1990). The optical irradiation system in this optical disk player decreases the light intensity near the center of the entrance pupil of a read laser beam using a light-shielding plate before forming the spot of a diffraction pattern on the surface of an optical disk, and utilizes a main lobe having a small spot size.
According to such a conventional optical disk player, the spot of the diffraction pattern of a laser beam, which is created by the shielding plate as shown in FIG. 1(a), contains secondary or higher components, i.e., side-lobe components as shown in FIG. 1(b). The side-lobe components extend to the adjoining pits, so that the reflected light has an undesirable crosstalk as shown in FIG. 1(c). According to the prior art, therefore, the width of the shielding portion and that of the transmitting portion in the optical irradiation system should be set in accordance with the radial distance between the side lobes that should be eliminated.
However, the above conventional optical disk player cannot sufficiently eliminate the side lobes of a diffraction pattern on the surface of an optical disk.